1. Field of the Invention
The present invention relates to a method and device for drying a container of the type such as a two piece can body which has an integrally formed bottom and peripheral wall, after it has been washed.
2. Description of the Prior Art
In recent years two piece beverage cans have come into wide use. The can body of these containers is usually made of tin plated or aluminium alloy sheet and formed by pressing such as drawing and ironing or deepdrawing. This is followed by trimming of the edge defined about the open end.
In order to remove lubricant used in the deep drawing or ironing steps, so as to ensure good adhesion of paint and the like, the can body is subjected to degreasing, water rinsing, chemical treatment, de-ionized water rinsing and then dried. Further, the internal and external surfaces of the can body are covered with organic coating films.
U.S. Pat. No. 3,574,952 issued on Apr. 13th, 1971 in the name of Lee, Jr. (corresponding Japanese first provisional publication JP-A-47-33348) discloses a device for drying can bodies and the like type of containers after they have been washed using water or de-ionized water.
In brief, the above mentioned drying device uses a chain conveyor and a hot drying chamber through which hot air is circulated. After the containers are washed they are placed on top of the chain conveyor with the open ends oriented downwardly and moved into the drying chamber. Jets of air which is heated to a predetermined temperature, are directed down onto the external surfaces of the containers through a flow diffusing member. A perforate plate is arranged below the chain conveyor on which the containers are supported and arranged to create a reduced pressure and to produce a venturi effect which induces some of the heated air to circulate up into the containers.
U.S. Pat. No. 3,952,698 issued on Apr. 27, 1976 in the name of Beyer et al. (corresponding Japanese first provisional publication JP-A-50-77440) discloses an arrangement wherein can bodies of the two piece can type are placed in an inverted condition (viz., with the open end oriented downwardly) on an open net or meshwork conveyor. Air is induced to flow down from an overhead source over the external surface of the containers. This procedure is such as to blow off excess water from the external surfaces of the containers and leave the same coated with a small amount of residual moisture. The reason for not completely drying the surfaces is that, by having a thin water film or moisture layer on the order of a few hundredths of mils thick, the adhesive affinity of the metal surfaces to a subsequent water based coating is alleged to be improved measurably depending on the material used.
However, these arrangements have suffered from one or more drawbacks. That is to say, in the arrangement disclosed in U.S. Pat. No. 3,574,952, the heated air is induced to flow downwardly onto the containers which are placed in an inverted position on the chain conveyor. This downward flow presses the containers down onto the conveyor and obviates the need for special apparatus to hold the same in place. Further, some of the heated air circulates up into the interior of the container and thus the interior of the container can be dried along with the external surface. However, some water droplets tend to remain within the containers and lead to the situation wherein they cause contaminates to be undesirably transferred from the chain conveyor which is in direct contact with the edge of the containers, into the interior of the containers. In addition to this problem, while the flow of air produced by the hot air jets blows off the water droplets on the external surfaces of the containers, the air flow within the containers is slower and insufficient to assuredly remove the water on the inner surfaces. Accordingly, in order for complete drying to be achieved, the containers must be exposed to the hot air sufficiently long for the residual water within the containers to be removed via evaporation. This of course tends to increase the drying time and slows the drying process.
Further, in connection with the arrangement disclosed in U.S. Pat. No. 3,952,698, even though air is directed into the interior of the containers, such an arrangement cannot be applied in situations wherein complete drying is demanded, as the process is not directed toward achieving complete drying.